Wax based emulsions are used in numerous industrial applications, for example, for coating fibrous cellulosic products, such as paper, corrugated cardboard, kraft paper, boxboard and the like, to impart moisture resistance to the product. Wax emulsions usually comprise between about 15% to 40% (by weight) wax, and with from about 5% to 25% surface-active agent added based on the weight of the wax. Emulsions are used in lieu of applying molten wax because of their ease of handling, application and ability to formulate with other aqueous based ingredients. Once prepared, an emulsion may remain stable (i.e., it will not separate into its components) over a prolonged period of time. This stability facilitates factors such as shipment of the emulsion from manufacturer to the end-user, storage, and its use in particular applications By contrast, application of molten wax requires that the wax be melted as needed, maintaining it in a molten state, and applying it in a molten state.
Wax emulsions are typically manufactured either in batch reactors or with the use of a homogenizer. It is important that the equipment used to prepare emulsions be capable of effecting agitation of the reactants to achieve thorough mixing, and have proper temperature controls to maintain adequate heating and cooling of the reagents and the products. In general, use of a homogenizer has been known to effect a higher percentage of solids in the final emulsion product than that obtained with emulsions prepared using mixing in conventional stirred batch reactors. Both types of equipment have been used successfully to manufacture the emulsions of the present invention.
It is desirable to utilize an emulsion that has as high a content of wax solids as practical for certain applications. For example, where goods such as paper products, fruits or pharmaceuticals are treated with a wax, it is desirable to minimize the drying time of the treated product, and one way to achieve this end is with the use of an emulsion having a high wax solids content. In those instances where the emulsions must be transported over long distances, reducing the volume amount helps to reduce transportation costs. Water based emulsions are also preferable to organic solvent based emulsions (or dispersions) of wax, because of the potential to pollute the environment or adversely affect health and safety.
Wax based emulsions are typically formulated to have a certain ionic charge, usually to render the emulsion compatible with other ingredients to be formulated with the wax emulsion at a later time. Wax emulsions can be either anionic, nonionic or cationic depending upon the emulsifier, generally a surface-active agent such as a surfactant, used to make the wax emulsion.
Waxes that are to be emulsified must have some functionality such as carboxyl, acid or ester groups attached to the wax polymer. In the process of emulsification these functional groups are saponified to render them more hydrophilic, thus allowing the selected surfactant to form a micelle around the wax. Bases that are commonly used to saponify functional groups of the wax include potassium hydroxide (KOH), sodium hydroxide (NaOH) and amines such as ammonia, diethyl amine (“DEA”) and other amine derivatives. For the preparation of certain emulsion types, acids, such as glacial acetic acid or similar acids, are utilized for functional group modification. The quantity of functional groups that need to be modified in order to form a stable emulsion can vary depending on characteristics of the wax such as its molecular weight and amount of chain branching. Generally, a wax with a minimum saponification value of about 20-30 mg KOH/g wax can be readily emulsified. The saponification value, or number, represents the quantity, in milligrams of KOH which react with one gram of wax under elevated temperatures, and indicates the amount of free carboxylic acid plus any esters which may be saponified. This value, and the acid number, described below, provide an indication of the free carboxylic acid and ester content of the wax. ASTM D1387 is an example of how a saponification number is determined. The ASTM D1386 represents a method to determine the acid number; the quantity, in milligrams, of KOH necessary to neutralize one gram of wax, indicating the amount of free carboxylic acid present.
A common first step in the emulsification process is to dissolve the wax (by heating where necessary) and add sufficient base to saponify the desired number of functional groups on the wax. Surfactant is then added and the emulsion is allowed to form under good agitation. If a homogenizer is used in manufacturing the emulsions the shearing action of the homogenizer also affects the resulting particle size of the wax emulsion. The saponification of the wax becomes less critical when emulsions are prepared using a homogenizer because of the contributions of mechanical shearing of the wax. In general, the most stable emulsions (generally having the smallest particle sizes) are produced with a combination of saponification with good mixing.
Parameters that usually characterize the quality of the emulsion once it has been formed include the clarity and stability of the emulsion. Stability is generally measured as the degree of separation of the emulsion into its component phases over time.
Hardness, defined by ASTM D1321 and ASTM D-5, relates to the distance (in tenths of a millimeter, dmm) that a specified needle penetrates a wax under a given weight at a given temperature. A “soft” wax has hardness properties of >10 mm of penetration, and are considered to be “less” useful, while waxes having hardness values of <10 mm penetration are considered to be more useful in these preparations.
The color of a particular wax preparation varies from batch to batch, even of the same wax. Factors such as the rate of cooling of the wax, the quantity of occluded air, and the surface finish affect the overall color of a solidified wax preparation. Generally, the color of a wax is determined on a molten wax preparation, using either the ASTM D1500 (Gardner) or the ASTM D156 (Seybolt) method. The ASTM D1500 method is generally used to measure dark-brown to off-white colors, while the ASTM D156 is used for measurement of off-white to pure white colors.
For applications such as coating of foods, or of pharmaceutical tablets, it is desirable to use waxes that are characterized by having low penetration hardness, and good color characteristics (towards the white end of the color scale as opposed to the brown end).
Wax emulsions are often used by themselves, or in combination with other ingredients when coated onto paper, paperboard, linerboard, or other paper products to render it moisture resistant. Food items, such as fish, or vegetables such as broccoli, for example, are often packaged and shipped in paper boxes that are coated with wax. The wax coating helps to maintain the strength and integrity of the package when it encounters a moist environment, such as the presence of ice in the package, transportation in refrigerated vehicles, and refrigerated storage environments. Other properties, such as the gloss, slip resistance and printability on or of the finished paper product, depending on the end use application, also are affected by a wax coating. Once the wax coated packaging has been used, it is generally discarded.
There is an increasing trend, both domestically and internationally, to recycle paper products once the packaged item is used and the wax-coated packaging has been disposed by the consumer. However, in the recycling process the wax coating on the packaging tends to form what is known in the, industry as “stickies” and “tackies”, whose presence causes problems in the recycling equipment. This problem has become so prevalent that in some localities wax coated paper products are required to be excluded from the recycling process. Consequently, the wax-coated articles are segregated, and instead of being recycled, are sent either to be incinerated or disposed of in landfills. Alternate techniques have been proposed and used to minimize wax contamination of the recycling process, including the use of additives added to the wax, (U.S. Pat. Nos. 6,255,375 and 6,273,993 to Michelman; U.S. Pat. No. 6,416,620 to Narancic et al.; and U.S. Pat. No. 6,053,439 to Locke et al.). None of these approaches has been universally accepted as a solution to the problems associated with wax in the recycling process.
Oil companies such as CITGO, ExxonMobil, Shell Oil and others are among the commercial sources for waxes derived from petroleum Most of these waxes are derived in the process of refining lube oil, where the wax is separated from the lube oil stock and refined into various wax fractions, including paraffins and microcrystalline waxes. Additional commercial sources of waxes include formulators such as Astor Wax, IGI and Moore & Munger, who supply wax for prior art applications; these axes are often either resold “as is” from the oil companies, and/or formulated and repackaged to meet specific customer needs. Other commercial suppliers, such as Michelman (Ohio) and ChemCore (New York), often referred to as “emulsion houses” convert various waxes into emulsions which are used for coating and other applications.
The prior art describes using petroleum-derived waxes and synthetic waxes for incorporation into emulsions, but does not mention using vegetable-derived waxes in emulsions. Given that the world's oil supply is finite, and is being depleted, there is a recognized and long-felt need to find alternatives to petroleum-derived products, such as petroleum waxes, that are derived from limited natural resources whose supply is being diminished. Because wax emulsions are frequently used in food packaging applications, it is also desirable for the wax to have food grade properties for safety. There is also a recognized and long-felt need to use materials in emulsions that are naturally derived and can be easily recycled back into the environment without long-term adverse effects; corrugated cartons having wax-based coatings and adhesives, for example, are known to be difficult to recycle. Therefore, there is a need for employing a wax, which has similar properties of petroleum derived or synthetic waxes used in emulsion formulations. Due the large volume of waxes consumed in these applications it is also preferred that the compositions be readily available. From both a supply and a natural resource viewpoint, it is preferred that the compositions be obtained from a source that preferably is renewable, such as from plant extracts. Thus it is desirable to have a wax that does not have to be imported, and which can be produced at a cost that is competitive with that of petroleum-derived waxes, such as the paraffins and microcrystalline waxes.
There is a need for a wax that can be converted into anionic, cationic or nonionic emulsions, has a relatively high melting point, low viscosity, has good moisture barrier properties and is thermally stable. It is also desirable to have a wax that can be obtained from a renewable source, such as plants, rather than being petroleum based because of the previously discussed world's petroleum supply. The waxes used in the present invention meet these requirements.
The present invention relates to emulsions prepared using a vegetable wax comprising triglycerides, and having a melting point of from about 136-200 degrees F. (57.8-94 degrees C.). These wax emulsions are used in a variety of applications including coating paper and wood, in polish and cosmetic applications, in inks, paints and adhesives; and in fruit coatings and in gypsum products to improve moisture resistance.
The present invention relates to a family of waxes derived by hydrogenating one or more vegetable oils. When hydrogenated to a high degree the properties of the oils are modified and become wax—like, having high melting points, low viscosities and good hardness. The waxes of the present invention are unique in that they also possess a high degree of functional groups. By modifying a portion of the functional groups on the present waxes they can be readily emulsified. Additionally it has unexpectedly been discovered that the waxes of the present invention can also be readily recycled due to the ability to further saponify the functional groups on the wax thereby rendering the wax more hydrophilic. Yet another unexpected discovery is the ability of the saponified waxes to help separate out inks and adhesive trash during the recycling process due to the relatively low density of the waxes and their ability to float and carry the ink, adhesive and trash with the wax.
The wax emulsions are comprised primarily of water, a surface-active agent (which will be either cationic, nonionic or anionic, depending upon the properties desired for the particular emulsion) and either an acid or a base (often chosen from KOH, NaOH, or one of a variety of amines. Other ingredients such as biocides or stabilizers may be added, as are well known to those versed in the art. Biocides, and/or antimicrobial agents may be added to the emulsion, the choice of a particular biocide or antimicrobial often being dependent upon the end use of the emulsion. Parabens such as methyl or ethyl hydroxy parabenzoic acid, or quaternary ammonium compounds, are among the biocides which may be used, other compounds being known to those skilled in the art. Because the waxes used in the preparation of the present invention are naturally occurring, readily. available, generally regarded as safe and have relatively high melting points with good hardness and color, they can be used in lieu of less desirable synthetic waxes (often derived from petroleum, such as polyethylene) or in lieu of other less available naturally occurring waxes, such as, for example only, montan or carnauba.
Additionally, the waxes employed in the present invention can be readily removed from articles to which they have been applied, such as boxboard and paper. This removal is effected under what are considered to be normal conditions for paper recycling (dispersal in a warm alkaline aqueous mixture with agitation), because these waxes have been readily modified. Further, the present inventors have found that because of the relatively low density of the waxes employed in the present invention, that separation of inks and other trash during the paper recycling process are enhanced as the wax floats away from the paper, carrying inks and other recycling trash with it for easy skimming and removal in a paper recycling process. The ease of removal of these waxes from treated goods makes emulsions containing them suitable for use in textile applications where the lubrication and or sizing properties of the wax may be needed, such as in the process of fiber spinning and or fabric weaving, yet their removal is desirable at a later stage such as dying or de-sizing. The biodegradability of the novel waxes makes them particularly suitable for discharge to waste treatment plants capable of handling natural organic materials. Application of the novel wax emulsions to fruit has also been shown to have beneficial properties through their ability to reduce moisture loss and extend produce shelf life.
The present invention describes natural waxes which are used to formulate emulsions. The waxes are commercially available, high triglyceride waxes, derived from the processing of natural oil-containing commodities such as soybeans, palm, castor, canola and other crops from which oil can be obtained. Vegetable oils having differing degrees of hydrogenation are used in the food industry. For purposes of cooking oils, unsaturated oils are preferred. The highly hydrogenated waxes employed in the present invention, while commercially available, are not widely produced or used because of their limited applications in the food industries. The waxes used in the present invention are commercially available. Materials are processed and supplied by Archer Daniels Midland (Decatur Ill.) designated by their product number 86-197-0, Cargill Incorporated (Wayzata, Minn.) designated by their product number 800mrcs0000u and other sources under a generic name ‘hydrogenated soybean oil’. Palm oil wax was supplied by Custom Shortenings & Oils (Richmond, Va.) and was designated as their product Master Chef Stable Flake-P. A mixture of hydrogenated castor oil and soy wax was also obtained from the Abitec Group (Columbus, Ohio, a blender and formulator of vegetable oil derived waxes), sold under the STEROTEX® trademark.